The aesthetic, morphological and functional rehabilitation of the oro-maxillo-facial area has reached high standards in recent decades, due to the progress of all disciplines related to dentistry, such as anesthesiology, microsurgery and pharmacology.
However, bone loss is still the limiting step in order to reach a good rehabilitation. Bone loss can be classified regarding the site (i.e. related to the periodontium, jaws, cranio-maxillo-facial area, etc), the quality, the embryological origin, the mechanical bone properties (related to the strength of cancellous bone; Trisi P. And Rao W. Bone classification: clinical-histomorphometric comparison. Clin. Oral Implants Res. 1999, 10:1-7) and the quantity (that can be defined as the total volume of lost bone).
The lost bone can involve the periodontal area, jaws, cranio-facial skeleton and sites of different part of the body. Several are the causes involved:
1—Deficit of anatomical structures fixing the teeth to jaws. The teeth are fixed in the alveolar bone by means of periodontium, composed of gingiva, cement, periodontal ligament and alveolar bone. Periodontal diseases are many illnesses due to genetic and environmental factors. The clinical sign is an alveolar bone resorption and a loss of teeth attachment. The degree of illness is scored as vertical bone loss and number of alveolar walls involved. As the maximum length of dental root is around 20 mm, the maximum vertical bone loss with teeth still in place cannot be higher (Lindhe J., Parodontologia, Edi-Ermes, Milano, 1991). Periodontal diseases are epidemic. In some geographical areas, more than 10% of the population has periodontal pockets which can be probed more than 5 mm (Orozco A. H. et al., Periodontal treatment needs in a native island community in Columbia. Int. Dent. J. 2004, 54: 73-76). All these patients need a specific therapy to restore the lost alveolar bone.
2—Deficit of bone in the jaws. These deficits have several causes, such as partial or total edentulism (that causes alveolar bone resorption), trauma and tumors. Among tumors, the oral squamous cell carcinoma is the most frequent malignant disease of the mouth with about 30,000 new cases and 8,000 dead patients per year in US (Greenlee R., et al. Cancer statistic. Cancer J. Clin. 2001, 51: 15-36). As regard the facial traumas no national report is still available, but the number of treated patients is very high if one considers that a single center can operate more than 1,000 patients per year (Gassner R. et al. Cranio-maxillo-facial trauma: a 10 year review of 9,543 cases with 21,067 injures. J Craniomaxillofacial Surg. 2003, 31: 51-61).
3—Deficit of Bone in the Craniofacial Area.
There are several causes which determine bone loss. Among them are post-traumatic sequelae, craniofacial resection for tumor removal and malformations. Examples of congenital malformations which require autologous bone grafts are cleft of lip and palate (in this case the autologous bone graft is inserted in the cleft of the alveolar ridge) and the Treacher Collins syndrome (in this case a rib is used to restore the mandible).
4—Deficit of Bone Tissue Outside the Head Region.
There are several causes which determine bone loss. Among them are post-traumatic sequelae, bone resection for tumor removal and malformations. In all these cases the availability of autologous bone to restore the deficit is the limiting step that orthopedics have to overcome in the daily practice.
As reported above, the bone deficit can be classified as minor (as in the periodontal disease) if the bone volume defect is roughly a few millimeters per side and major if the bone loss is bigger.
Today to correct bone defects there are several biomaterials and different surgical techniques. All of them have advantages and disadvantages.
In minor bone defects, there are several medical and surgical procedures to prevent and restore the periodontal disease. However, when the periodontal diseases are severe, we need to restore the bone deficit. This can be reached by using alloplastic or eterolog/xenograft material. Both can produce osteo-induction and/or osteo-conduction. In the same cases the dentist can use membranes which determine a physical separation between epithelium and the underlining bone.
In major bone defects there are three therapeutic possibilities: 1) use alloplastic material (such as mash to reconstruct the mandible or hip prosthesis), 2) use autologous bone graft (such as the iliac crest graft to rebuilt the mandibular arch or free flaps collected from fibula, forearm, iliac crest, etc.), 3) distraction osteogenesis.
In any case, the golden standard is the use of autologous bone. The use of eterologous or xenograft bone can lead to non-self reaction and also to unknown disease transmission, whereas the use of alloplastic materials cannot restore the deficit and moreover is prone to induce infections and foreign-body reactions. Today, there are several limits to an extensive use of autologous bone grafts: 1) the morbility in the donor site (i.e. fibula, forearm, iliac crest, etc) is not always acceptable overall if one considers that sometimes the graft failed; 2) the surgical strategy has relevant costs with regards to instruments and equipe training; 3) the collection of the graft from the donor site enlarges the operation time; 4) it is not possible to collect a high amount of bone from the donor site since it can cause sequelae in it.
Taking into account what above reported, one can conclude that: 1) the bone deficit is the limiting step in the dental, maxillo-facial and orthopedic reconstruction; 2) the autologous bone is the gold standard; 3) to collect autologous bone from a different site of the same patient leads to additional risks for the patient itself, requiring a specific equipe training and has biological and economic costs.
A potential solution to these adverse factors is the use of an autologous bone produced in vitro by using specific cytotypes. From this point of view, the use of stem cells (that are able to differentiate in osteoblasts producing bone in vitro) can be a good strategy.
Stem cells are cells characterized by: 1) self-renewal (i.e. no limit to the potential number of cell division); 2) commitment and differentiation to different cell lines. In literature it has been reported the identification of stem cells derived from bone marrow and able to differentiate in osteoblasts (Kuznetsov S. A., et al. Single-colony derived strains of human marrow fibroblasts from bone after transplantation in vivo. J. Bone Min. Res. 1997; 12, 1335-47; Pittenger M. F., et al. Multilineage potential of adult human mesenchymal stem cells. Science 1999, 284, 143-147), but it is not described the capacity of these cells (named Bone Marrow Stromal Stem Cells—BMSSC) of producing bone in a three-dimensional structure in vitro. More recently, the isolation and characterization of stem cells, derived from human dental pulp has been described. (Gronthos S. et al., PNAS 2000, 97, 13625-13630; Gronthos S. et al., JDR 2002, 81, 531-535; Batouli S. et al., JDR 2003, 82, 976-981; US n. 20040058442 di Shi et al.). Specifically, the Dental Pulp Stem Cell (DPSC) line is a precursor of osteoblasts and is characterized by: 1) the presence of specific dentin sialoprotein; 2) the absence of bone production in vitro; 3) the production of dentin-like structures in vivo, when cells were transplanted in immuno-deficient mice.
Miura M et al. (PNAS 2003; 100, 5807-5812) describe an additional class of stem cells obtained from deciduous dental pulp, called Stem Cells from Human Exfoliated Deciduous teeth (SHED). SHED cells can differentiate in osteoblasts in vitro but they need the addition of BMP-4 to the medium. Moreover SHED cells do not differentiate in osteoblasts when transplanted in immuno-deficient mice. Both SHED and DPSC cells are unable to produce bone tissue in vitro.
In addition both SHED and DPSC need a ceramic vector in order to be transplanted in the animal to obtain a three-dimensional tissue.
Additional patents, related to the state of the art of the present invention, are the US n. 20020119180 (by Yelic et al.) and the US n. 20030068305 (by Sramek et al.). The US n. 20020119180 describes a method to produce dental germ in an animal model. These dental germs can be potentially inserted in human gum to replace lost teeth. The US n. 20030068305 describes a method and a specific tool to collect the dental pulp.